U.S. patent application number 11/137615 was filed with the patent office on 2005-09-29 for pressure activated fingerprint input apparatus.
This patent application is currently assigned to CASIO COMPUTER CO., LTD.. Invention is credited to Sawano, Tomomi.
Application Number | 20050213799 11/137615 |
Document ID | / |
Family ID | 34989849 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050213799 |
Kind Code |
A1 |
Sawano, Tomomi |
September 29, 2005 |
Pressure activated fingerprint input apparatus
Abstract
An image input apparatus includes an image reading assembly
positioned below a placement surface on which an object to be
examined is placed, and a sensing circuit for sensing that the
object is placed on the placement surface, in accordance with a
pressure applied to the placement surface.
Inventors: |
Sawano, Tomomi; (Fussa-shi,
JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 5TH AVE FL 16
NEW YORK
NY
10001-7708
US
|
Assignee: |
CASIO COMPUTER CO., LTD.
Tokyo
JP
|
Family ID: |
34989849 |
Appl. No.: |
11/137615 |
Filed: |
May 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11137615 |
May 24, 2005 |
|
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PCT/JP03/15845 |
Dec 11, 2003 |
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Current U.S.
Class: |
382/124 |
Current CPC
Class: |
G06K 9/0002
20130101 |
Class at
Publication: |
382/124 |
International
Class: |
G06K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2002 |
JP |
2002-368558 |
Claims
What is claimed is:
1. An image input apparatus comprising: an image reading assembly
having, on one side, a placement surface on which an object to be
examined is placed; and sensing means for sensing that the object
is placed on the placement surface, in accordance with a pressure
applied to the placement surface by the object.
2. An image input apparatus according to claim 1, which further
comprises driving means for causing the image reading assembly to
perform an image reading operation, when the sensing means senses
that the object is placed on the placement surface.
3. An image input apparatus according to claim 1, wherein the
sensing means comprises: a pressure sensor which senses a pressure
applied to the placement surface; and comparing means for comparing
a pressure level sensed by the pressure sensor with a threshold
value for discriminating between a placed state and unplaced state
and, if the threshold value is reached, outputting a trigger signal
for causing the image reading assembly to perform an image reading
operation.
4. An image input apparatus according to claim 3, which further
comprises a light source which illuminates the object with light on
the basis of the trigger signal.
5. An image input apparatus according to claim 1, which further
comprises adjusting means for adjusting brightness of the light
source for irradiating the object with light, in accordance with a
pressure applied to the placement surface by the object.
6. An image input apparatus according to claim 1, wherein the
placement surface has first and second regions, the image reading
assembly has the first region of the placement surface, and the
sensing means is positioned in the second region of the placement
surface.
7. An image input apparatus according to claim 6, wherein the first
region is a region where a portion beyond a first joint of a finger
is placed, and the second region is a region where a portion from a
second joint to a first joint of a finger is placed.
8. An image input apparatus according to claim 1, wherein the image
reading assembly has an optical sensor.
9. An image input apparatus according to claim 8, wherein the
optical sensor has a plurality of double-gate transistors arranged
in a matrix manner.
10. An image input apparatus according to claim 1, which further
comprises a holder which holds the object such that the object is
properly placed in. positions of the image reading assembly and
sensing means.
11. An image input apparatus comprising: an image reading assembly
having, on one side, a placement surface on which an object to be
examined is placed; and sensing means placed on the other side of
the image reading assembly to sense that the object is placed on
the placement surface, in accordance with a pressure applied to the
placement surface by the object.
12. An image input apparatus according to claim 11, which further
comprises driving means for causing the image reading assembly to
perform an image reading operation, when the sensing means senses
that the object is placed on the placement surface.
13. An image input apparatus according to claim 11, wherein the
sensing means comprises: a pressure sensor which senses a pressure
applied to the placement surface; and comparing means for comparing
a pressure level sensed by the pressure sensor with a threshold
value for discriminating between a placed state and unplaced state
and, if the threshold value is exceeded, outputting a trigger
signal for causing the image reading assembly to perform an image
reading operation.
14. An image input apparatus according to claim 11, which further
comprises light irradiating means for irradiating the object with
light, placed between the image reading assembly and sensing
means.
15. An image input apparatus according to claim 14, wherein the
light irradiating means has a diffusion light-guiding plate which
guides, to the object, light from a light source which emits light
when the object is sensed by the sensing means.
16. An image input apparatus according to claim 11, which further
comprises adjusting means for adjusting brightness of light for
irradiating the object with light, in accordance with a pressure
applied to the placement surface by the object.
17. An image input apparatus according to claim 11, wherein the
image reading assembly has an optical sensor.
18. An image input apparatus according to claim 17, wherein the
optical sensor has a plurality of double-gate transistors arranged
in a matrix manner.
19. An image input apparatus according to claim 11, which further
comprises a holder which holds the object such that the object is
properly placed in positions of the image reading assembly and
sensing means.
20. An image input apparatus comprising: sensing means for
outputting a sense signal in accordance with a pressure of a finger
when the finger is placed on the sensing means; a plurality of
sensor elements which are positioned below a fingerprint portion of
the finger when the finger is placed on the sensing means, and read
an image corresponding to projections and recesses of the finger;
and a driving circuit which starts an image reading operation of
said plurality of sensor elements in accordance with the sense
signal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation Application of PCT Application No.
PCT/JP03/15845, filed Dec. 11, 2003, which was published under PCT
Article 21(2) in Japanese.
[0002] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2002-368558,
filed Dec. 19, 2002, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to an image input apparatus
which includes an image reading circuit positioned below a
placement surface on which an object to be examined is placed, and
inputs an image of the object by reading the object by an image
reading device.
[0005] 2. Description of the Related Art
[0006] A fingerprint has a pattern unique to an individual and
hence is a very useful means for authenticating a person. Recently,
a fingerprint authentication apparatus which applies a fingerprint
to personal authentication is developed. More specifically, this
fingerprint authentication apparatus performs personal
authentication by comparing a fingerprint image read by an image
reader with fingerprint image data of a preregistered person. It is
being attempted to mount this fingerprint authentication apparatus
in information apparatuses such as a personal computer, PDA
(Personal Digital Assistance), and cell phone.
[0007] Jpn. Pat. Appln. KOKAI Publication No. 2002-94040 describes
a two-dimensional image reader to be used in the fingerprint
authentication apparatus. This two-dimensional image reader
includes a photosensor array in which a plurality of photosensors
are arranged on a transparent substrate, a backlight positioned at
the back of the photosensor array so as to oppose its rear surface,
a transparent electrode layer covering the surface of the
photosensor array, and a sensor for sensing a voltage change in the
electrode layer. The operation of the conventional two-dimensional
image reader and a method of using it will be explained below. When
a person to be examined places his or her finger on the electrode
layer, the sensor senses a unique voltage change caused by the
contact of the finger with the electrode layer, since the person
himself or herself has a unique resistance and capacitance. In
accordance with this finger sensing by the sensor, the backlight
illuminates the finger with light, and the photosensor array reads
an image of the finger by an image reading operation. This finger
image read by the photosensor array is represented by the intensity
distribution of reflected light from projections and recesses of
the finger on the contact surface.
[0008] A finger perspiration state differs from one person to
another, and a pressure with which a finger placed on the electrode
layer presses the electrode layer also differs from one person to
another. Different finger perspiration states cause different
unique voltage changes when these fingers come in contact with the
electrode layer. Similarly, different electrode layer pressing
forces of fingers cause different electrode layer voltage changes
because the contact areas between these fingers and the electrode
layer are also different. In the conventional two-dimensional image
reader, therefore, if the tolerance of variations in perspiration
state between individuals and the tolerance of variations in finger
pressure are too small, a finger of a certain person placed on the
electrode layer may not be sensed by the sensor and so a
fingerprint image of this person cannot be read, while a finger of
another person placed on the electrode layer can be sensed by the
sensor and so a fingerprint image of this person can be read. The
perspiration state or pressing force of a finger of even the same
person may change in some cases, so a fingerprint image of the
finger cannot be read in this case. Also, if the tolerance is too
large, an operation error may be caused by an object, other than a
finger, which comes in contact with the electrode layer. Likewise,
if the tolerance is extended to cover even weak electrode layer
pressing forces, projections of a finger do not come in close
contact with the electrode layer. Since the pattern of the
fingerprint cannot be clearly read in this case, accurate
authentication may not be performed. Furthermore, such very small
voltage changes cannot be accurately sensed owing to noise such as
ambient electromagnetic waves.
BRIEF SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide an image
input apparatus capable of simply and reliably reading an image and
capable of reading a clear image.
[0010] To achieve the above object, an image input apparatus
according to an aspect of the present invention comprises: an image
reading assembly having, on one side, a placement surface on which
an object to be examined is placed; and sensing means for sensing
that the object is placed on the placement surface, in accordance
with a pressure applied to the placement surface by the object.
[0011] In the invention of the above aspect, when an object to be
examined is placed on the placement surface, a pressure is applied
from the object to the placement surface. Since the sensing means
senses the placement of the object by the pressure applied to the
placement surface, a reading operation of the image reading circuit
can be stopped when no object to be examined is placed on the
placement surface, and can be immediately started when an object to
be examined is placed on the placement surface. Therefore, the
power consumption when no object to be examined is placed on the
placement surface can be reduced. Also, it is unnecessary to
perform any special operation except for placing a finger in order
to initiate a reading operation. Accordingly, an image of an object
to be examined can be reliably read only by placing the object on
the placement surface.
[0012] Also, when a finger is an object to be examined, it is
conventionally impossible to sense the placement of the finger in
some cases owing to, e.g., the perspiration state of the finger. In
the present invention, however, a pressure is applied to the
placement surface when a finger is placed on the placement surface,
so the sensing means can reliably sense the placement of the
finger. This makes it possible to reliably read a finger's
image.
[0013] The sensing means may comprise
[0014] a pressure sensor which senses a pressure applied to the
placement surface, and
[0015] comparing means for comparing a pressure level sensed by the
pressure sensor with a threshold value for discriminating between a
placed state and unplaced state and, if the threshold value is
reached, outputting a trigger signal for causing the image reading
circuit to perform an image reading operation.
[0016] When an object to be examined is placed on the placement
surface, a pressure is applied from the object to the placement
surface. However, if this pressure applied from the object to the
placement surface is low, the contact area between the object and
placement surface becomes small. Therefore, even if the image
reading circuit reads an image, no clear image can be read. With
this arrangement, however, unless the level of a sense signal
indicating the pressure applied from an object to be examined to
the placement surface is equal to or higher than a threshold value,
the comparing means outputs no trigger signal, so the image reading
circuit performs no image reading operation. Therefore, no such
unclear image is read. If the level of the sense signal indicating
the pressure applied from an object to be sensed to the placement
surface exceeds the threshold value, the comparing means outputs a
trigger signal, and the image reading circuit performs an image
reading operation. As a consequence, the image reading circuit
reads an image when the contact area between an object to be
examined and the placement surface is sufficiently large, so a
clear image can be reliably read.
[0017] When the invention of the above aspect comprises adjusting
means for adjusting the brightness of a light source for
irradiating the object with light, in accordance with a pressure
which the object applies to the placement surface, the irradiation
intensity by the light source is adjusted on the basis of the
pressure applied to the placement surface by the object, so light
having intensity matching the contact area between the object and
placement surface is incident on the object. Accordingly, an image
of the object can be clearly read regardless of the contact
pressure applied by the object.
[0018] An image input apparatus according to another aspect of the
present invention comprises: an image reading assembly having, on
one side, a placement surface on which an object to be examined is
placed; and sensing means placed on the other side of the image
reading assembly to sense that the object is placed on the
placement surface, in accordance with a pressure applied to the
placement surface by the object.
[0019] In this structure, the sensing means can stop a reading
operation of the image reading circuit when no object to be
examined is placed on the placement surface, and can immediately
start a reading operation of the image reading circuit when an
object to be examined is placed on the placement surface. In
addition, since the sensing means is positioned below the image
reading circuit, the two-dimensional size of the image input
apparatus can be decreased. Therefore, this image input apparatus
is particularly effective as an authentication apparatus of a
highly portable device.
[0020] An image input apparatus according to still another aspect
of the present invention comprises: sensing means for outputting a
sense signal in accordance with a pressure of a finger when the
finger is placed on the sensing means; a plurality of sensor
elements which are positioned below a fingerprint portion of the
finger when the finger is placed on the sensing means, and read an
image corresponding to projections and recesses of the finger; and
a driving circuit which starts an image reading operation of the
plurality of sensor elements in accordance with the sense
signal.
[0021] As described above, the plurality of sensor elements are so
arranged that they are positioned below a fingerprint portion of a
finger when the finger is placed on the sensing means. This makes
an easy image reading operation feasible. In addition, when no
finger is placed on the sensing means, the sensor elements perform
no image reading operation, so the power consumption can be
reduced.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0022] FIG. 1 is a plan view showing a fingerprint reader to which
an image input apparatus of an embodiment of the present invention
is applied;
[0023] FIG. 2A is a sectional view taken along a line (II)-(II) in
FIG. 1 and showing the state in which no finger is placed, and FIG.
2B is a sectional view taken along the line (II)-(II) in FIG. 1 and
showing the state in which a finger is placed;
[0024] FIG. 3 is a sectional view taken along a line (III)-(III) in
FIG. 1 and showing an image reading circuit of the fingerprint
reader;
[0025] FIG. 4A is a plan view showing one pixel of the image
reading circuit, and FIG. 4B is a sectional view taken along a line
(IVB)-(IVB);
[0026] FIG. 5 is a block diagram showing the circuit configuration
of the fingerprint reader;
[0027] FIG. 6A is a sectional view showing the state in which no
finger is placed on a fingerprint reader different from the above
fingerprint reader, and FIG. 6B is a sectional view showing the
state in which a finger is placed;
[0028] FIG. 7 is a sectional view showing the fingerprint reader
shown in FIGS. 6A and 6B; and
[0029] FIG. 8 is a block diagram showing the circuit configuration
of the fingerprint reader shown in FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Embodiments of the present invention will be described below
with reference to the accompanying drawing. However, the scope of
the invention is not limited to these embodiments shown in the
drawing.
[0031] [First Embodiment]
[0032] FIG. 1 is a plan view showing a fingerprint reader 1 to
which an image input apparatus of the present invention is applied.
FIGS. 2A and 2B are sectional views taken along a line (II)-(II) in
FIG. 1 and showing the state in which no finger is placed and the
state in which a finger is placed, respectively. FIG. 3 is a
sectional view taken along a line (III)-(III) in FIG. 1.
[0033] The fingerprint reader 1 has an image reading circuit 2 or
image reading assembly which reads a fingerprint image of a portion
of a finger FN beyond the first joint placed on a contact surface
32a, by converting the amount or intensity of light reflected by
the finger FN and that of light transmitted through the finger FN
into electrical signals. The image reading circuit 2 is obtained by
integrating a solid-state image pickup device and its drivers, and
includes the contact surface 32a on one side, in this embodiment,
the upper side. The fingerprint reader 1 also comprises a driving
circuit 10 for acquiring fingerprint image data of the finger FN by
sensing the electrical signals from the image reading circuit 2, a
light irradiating means for irradiating the finger FN placed on the
contact surface 32a of the image reading circuit 2 with light, a
film-type pressure sensor 50 for sensing a pressure generated when
a portion of the finger FN from the second joint to the first joint
comes in contact with the sensor, and a finger holder 16 for
holding the finger FN in a predetermined position in the image
reading circuit 2 and pressure sensor 50.
[0034] First, the light irradiating means will be explained below.
The light irradiating means includes, a light source 14 such as an
LED for emitting light or a cold cathode fluorescent lamp, and a
diffusion light-guiding plate 15 for guiding light emitted from the
light source 14 to the image reading circuit 2, and irradiating the
finger FN as an object to be examined with the light via the image
reading circuit 2. The diffusion light-guiding plate 15 is a
substantially flat plate and is covered with a light-reflecting
material (not shown) except for one side surface facing the light
source 14 and one surface or the upper surface facing the rear
surface of the image reading circuit 2. The light from the light
source 14 enters the diffusion light-guiding plate 15,
two-dimensionally diffuses in the diffusion light-guiding plate 15,
and is two-dimensionally radiated from the surface of the diffusion
light-guiding plate 15. The rear surface of the image reading
circuit 2 is evenly irradiated with this light. Instead of the
diffusion light-guiding plate 15 and light source 14, a surface
light-emitting element such as an organic EL element may also be
disposed so as to oppose the rear surface of the image reading
circuit 2.
[0035] The image reading circuit 2 will be explained below with
reference to FIGS. 1 to 4B. FIG. 4A is a plan view showing one
pixel of the image reading circuit 2. FIG. 4B is a sectional view
taken along a line (IVB)-(IVB) in FIG. 4A.
[0036] The image reading circuit 2 includes a substantially flat
transparent substrate 17, photosensor elements (to be referred to
as sensor elements hereinafter) 20 which are a plurality of
N-channel double-gate transistors arranged into a matrix of n
rows.times.m columns on one surface or the upper surface of the
transparent substrate 17, a top gate driver 11, bottom gate driver
12 and data driver 13 formed around an image input region 8 in
which the sensor elements 20 are arranged on the transparent
substrate 17; a protective insulating film 31 for covering the
drivers 11, 12, 13 and sensor elements 20; and an antistatic film
32 formed on the protective insulating film 31.
[0037] The transparent substrate 17 has transmitting properties (to
be simply referred to as transparency hereinafter) to light having
a wavelength region which can be sensed by the sensor elements 20,
of the light emitted from the light source 14, has insulating
properties, and can be formed by a glass substrate such as quartz
glass or a plastic substrate such as polycarbonate. The transparent
substrate 17 forms the rear surface of the image reading circuit 2.
The diffusion light-guiding plate 15 faces the transparent
substrate 17.
[0038] Each sensor element 20 is a photoelectric conversion element
serving as a pixel, and includes a bottom gate electrode 21 formed
on the transparent substrate 17, a bottom gate insulating film 22
formed on the bottom gate electrode 21, a semiconductor film 23 so
formed as to sandwich the bottom gate electrode 21 with the bottom
gate insulating film 22 and facing the bottom gate electrode 21, a
channel protective film 24 formed by silicon nitride on a central
portion of the semiconductor film 23, impurity-doped semiconductor
films 25 and 26 formed apart from each other on the two end
portions of the semiconductor film 23, and a source electrode 27
and drain electrode 28 formed on the impurity-doped semiconductor
films 25 and 26, respectively. A top gate insulating film 29 is
formed on exposed surfaces of the bottom gate insulating film 22
and channel protective film 24 including the upper surfaces of the
source electrode 27 and drain electrode 28. Top gate electrodes 30
are formed on the top gate insulating film 29 so as to sandwich
with the semiconductor films 23, the top gate insulating film 29
and channel protective films 24 and respectively face the
semiconductor films 23.
[0039] The bottom gate electrodes 21 are arranged in a matrix
manner on the transparent substrate 17 in one-to-one correspondence
with the sensor elements 20 arranged in a matrix manner. On the
transparent substrate 17, n bottom gate lines 41 are formed to run
in the lateral direction. The bottom gate electrodes 21 of the
sensor elements 20 in the same column in the lateral direction are
integrated with a common bottom gate line 41. The bottom gate
electrodes 21 and bottom gate lines 41 have conductivity and light
shielding properties, and are made of, e.g., chromium, a chromium
alloy, aluminum, an aluminum alloy, or an alloy of these
metals.
[0040] On the bottom gate electrodes 21 and bottom gate lines 41,
the bottom gate insulating film 22 common to all the sensor
elements 20 is formed. The bottom gate insulating film 22 has
insulating properties and transparency, and is made of, e.g.,
silicon nitride or silicon oxide.
[0041] On the bottom gate insulating film 22, the semiconductor
film 23 is formed for each sensor element 20. Each semiconductor
film 23 assumes a substantially rectangular shape when viewed from
above. The semiconductor film 23 is a layer which is made of
amorphous silicon or polysilicon and generates electron-hole pairs
when irradiated with light having a predetermined wavelength
region. The channel protective film 24 formed on the semiconductor
film 23 has a function of protecting the interface of the
semiconductor film 23 from an etchant used in patterning. The
channel protective film 24 has insulating properties and
transparency, and is made of, e.g., silicon nitride or silicon
oxide. When light enters the semiconductor film 23, electron-hole
pairs are generated in an amount corresponding to the incident
light amount around the interface between the channel protective
film 24 and semiconductor film 23. Of the generated carriers, the
holes are held in the semiconductor film 23 and channel protective
film 24 in accordance with electric fields of the bottom gate
electrode 21 and top gate electrode 30.
[0042] The impurity-doped semiconductor film 25 on one end portion
of the semiconductor film 23 partially overlaps the channel
protective film 24. Likewise, the impurity-doped semiconductor film
26 on the other end portion of the semiconductor film 23 partially
overlaps the channel protective film 24. The impurity-doped
semiconductor films 25 and 26 are patterned for each sensor element
20. The impurity-doped semiconductor films 25 and 26 are made of
amorphous silicon (n.sup.+ silicon) containing n-type impurity
ions.
[0043] The source electrode 27 and drain electrode 28 are formed by
patterning on the impurity-doped semiconductor films 25 and 26 for
each sensor element 20. On the bottom gate insulating film 22, m
reference voltage lines 42 and data lines 43 are formed to run in
the longitudinal direction. The source electrodes 27 of the sensor
elements 20 in the same column running in the longitudinal
direction are integrated with a common reference voltage line 42,
and the drain electrodes 28 of the sensor elements 20 in the same
column running in the longitudinal direction are integrated with a
common data line 43. The source electrodes 27, drain electrodes 28,
reference voltage lines 42, and data lines 43 have conductivity and
transparency, and are made of, e.g., chromium, a chromium alloy,
aluminum, an aluminum alloy, or an alloy of these metals.
[0044] The top gate insulating film 29 common to all the sensor
elements 20 is formed on the channel protective films 24, source
electrodes 27, drain electrodes 28, reference voltage lines 42, and
data lines 43 of all the sensor elements 20. The top gate
insulating film 29 has insulating properties and transparency, and
is mode of, e.g., silicon nitride or silicon oxide.
[0045] On the top gate insulating film 29, the top gate electrode
30 patterned for each sensor element 20 is formed. n top gate lines
44 running in the lateral direction are formed on the top gate
insulating film 29. The top gate electrodes 30 of the sensor
elements 20 in the same row running in the lateral direction are
integrated with the top gate lines 44. The top gate electrodes 30
and top gate lines 44 are conductors having conductivity and
transparency, and are made of, e.g., indium oxide, zinc oxide, tin
oxide, or a mixture (e.g., tin-doped indium oxide (ITO) or
zinc-doped indium oxide) containing at least one of these
compounds.
[0046] The sensor element 20 constructed as above is a
photoelectric conversion element having the semiconductor film 23
as a light receiving portion.
[0047] On the top gate electrodes 30 and top gate lines 44 of all
the sensor elements 20, the common protective insulating film 31 is
formed in contact with the top gate electrodes 30 and top gate
lines 44. The protective insulating film 31 has insulating
properties and transparency, and is made of silicon nitride or
silicon oxide.
[0048] The antistatic film 32 is formed on the entire surface of
the protective insulating film 31. The antistatic film 32 has
conductivity and transparency, and is made of, e.g., indium oxide,
zinc oxide, tin oxide, or a mixture (e.g., tin-doped indium oxide
(ITO) or zinc-doped indium oxide) containing at least one of these
compounds. The antistatic film 32 is grounded and held at 0 (V),
and removes static electricity of the finger FN, thereby preventing
destruction of the sensor elements 20, top gate driver 11, bottom
gate driver 12, and data driver 13 by static electricity. The
contact surface 32a of the antistatic film 32 forms that surface of
the image reading circuit 20, with which the finger FN comes in
contact.
[0049] In the image reading circuit 2 described above, a portion of
light entering the transparent substrate 17 from the diffusion
light-guiding plate 15 is shielded by the bottom gate electrode 21
and hence does not directly enter the semiconductor film 23. Since
the bottom gate electrodes 21 are not formed between the sensor
elements 20, the remaining portion of the light is transmitted
through these portions between the sensor elements 20 and emitted
outside from the surface of the image reading circuit 2.
[0050] The drivers of the image reading circuit 2 will be described
below. As shown in FIG. 1, the reference voltage lines 42 are held
at a constant voltage, e.g., grounded and held at 0 (V). The bottom
gate lines 41 are connected to the outputs of the bottom gate
driver 12. The top gate lines 44 are connected to the outputs of
the top gate driver 11.
[0051] The top gate driver 11 is a shift register, and outputs a
reset signal in turn from the top gate line 44 in the first row to
the top gate line 44 in the nth row (when the nth row is reached,
the processing returns to the first row if necessary). When the
reset signal is output to the top gate line 44 in a certain row,
the top gate line 44 is set at a high-level reset potential which
removes holes stored in the semiconductor films 23 and channel
protective films 24. When the reset signal is not output to the top
gate line 44 in a certain row, the top gate line 44 and the top
gate electrodes 30 connected thereto are set at a low-level carrier
storage potential which holds holes of electron-hole pairs
generated by light entering the semiconductor films 23.
[0052] The bottom gate driver 12 is a shift register, and outputs a
high-level read signal in turn from the bottom gate line 41 in the
first row to the bottom gate line 41 in the nth row (when the nth
row is reached, the processing returns to the first row if
necessary). When the read signal is output to the bottom gate line
41 in a certain row, the bottom gate line 41 and the bottom gate
electrodes 21 connected thereto are set at a read potential by
which channels are formed in the semiconductor films 23. The size
of each channel region depends upon the amount of light entering
the semiconductor film 23.
[0053] The top gate driver 11 and bottom gate driver 12 shift their
output signals such that after the top gate driver 11 outputs the
reset signal to the top gate line 44 in the ith row (i is an
integer from 1 to n), the bottom gate driver 12 outputs the read
signal to the bottom gate line 41 in the ith row.
[0054] The data driver 13 outputs a pre-charge signal at a
predetermined level (high level) to all the data lines 43 from the
output timing of the reset signal to the output timing of the read
signal. In addition, after outputting this pre-charge signal, the
data driver 13 amplifies the voltage of the data lines 43, and
outputs this amplified voltage to the driving circuit 10.
[0055] The driving circuit 10 will be explained below.
[0056] The driving circuit 10 outputs a control signal Bcnt to the
bottom gate driver 12 to allow the bottom gate driver 12 to
appropriately output the read signal, outputs a control signal Tcnt
to the top gate driver 11 to allow it to appropriately output the
reset signal, and outputs a control signal Dcnt to the data driver
13 to allow it to appropriately output the pre-charge signal. Also,
the driving circuit 10 detects the voltage of the data lines 43
when a predetermined time has elapsed after the read signal is
output, or detects the time from the output timing of the read
signal to the timing at which the voltage of the data lines 43
reaches a predetermined threshold voltage, thereby acquiring a
fingerprint image of the finger FN.
[0057] The pressure sensor 50 will be described below.
[0058] As shown in FIG. 2A, the pressure sensor 50 includes a
plurality of electrode lines 51 arranged adjacent to the image
reading circuit 2 on the transparent substrate 17, formed on the
transparent substrate 17, and running parallel to each other in the
row direction, spacers 53 formed between the adjacent electrode
lines 51 on the transparent substrate 17 and higher than the
electrode lines 51, a flexible sheet member 55 on the rear surface
of which a plurality of electrode lines 52 running parallel to each
other in the column direction are formed, and a seal 54 which
covers the perimeter of the sheet member 55 and adheres the
transparent substrate 17 and sheet member 55. The electrode lines
52 are separated from the electrode lines 51 by the spacers 53. The
sheet member 55 and transparent substrate 17 are adhered such that
the electrode lines 51 and 52 are perpendicular to each other when
viewed from above and oppose each other. The spacers 53 may also be
arranged between the electrode lines 52 on the rear surface of the
sheet member 55. The spacers 53 need not always be formed if there
is an enough restoring force with which the electrode lines 51 and
52 can be separated with no pressure applied after the pressure
sensor 50 is repetitively pressed by a finger.
[0059] A sensing circuit 61 (to be described later) outputs a
voltage to at least one of the electrode lines 51 and 52 of the
pressure sensor 50. As shown in FIG. 2B, when the finger FN is
placed on the image reading circuit 2 and pressure sensor 50, the
pressure of the finger FN makes the sheet member 5 bend, and thus
the electrode lines 52 bend downward to contact the electrode lines
51 accordingly. As a consequence, the electrode lines 51 and 52
electrically connect to each other. This changes the electrical
characteristics such as an electric current flowing through the
electrode lines 51 and 52, the voltage or resistance of at least
one of the electrode lines 51 and 52. This change in electrical
characteristics is so designed as to be proportional to the force
with which the finger FN presses the pressure sensor 50. Therefore,
when the sensing circuit 61 senses an electrical characteristic
change to such an extent that the finger FN well presses the
pressure sensor 50, it is determined that the tip of the finger FN
is placed on the image reading circuit 2, so the light source 14
emits light to start a reading operation of the image reading
circuit 2. If the finger FN is not in close contact with the image
reading circuit 2 because the finger FN is not enough pressing the
pressure sensor 50, the electrical characteristic changes are
small, so the driving circuit 10 does not perform a reading
operation of the image reading circuit 2. Accordingly, not only the
image reading circuit 2 does not read an image in which the
fingerprint pattern of the finger FN is unclear because the contact
is insufficient, but also the person to be examined can notice,
since the light source 14 does not emit light, that he or she is
not rejected by authentication but is not well pressing the finger
FN. Therefore, the person tries to well press the finger FN against
the pressure sensor 50 and image reading circuit 2 so that the
driving circuit 10 performs a reading operation of the image
reading circuit 2. Consequently, a clear image can be read, and
this allows easy authentication.
[0060] In the pressure sensor 50, a pressure-sensitive ink layer
may also be formed on the surface of at least one of the electrode
lines 51 and 52. In this case, pressure-sensitive ink layers
overlap each other at the intersections of the electrode lines 51
and 52. The electrical resistance between the electrode lines 51
and 52 depends upon a pressure applied to the pressure-sensitive
ink layers. If the pressure changes, the electrical resistance or
the like also changes. In the pressure sensor 50, the pressure at
the intersection of the electrode lines 51 and 52 can be sensed by
the electrical resistance or the like at the intersection. When the
pressure sensor 50 is viewed from above, intersections are arranged
in a matrix manner. Therefore, when the sensing circuit 61 measures
a change in electrical characteristics of the electrode line 51 or
52 at each intersection, it is possible to sense the longitudinal
pressure distribution and the whole longitudinal pressure. If the
sensing circuit 61 senses that the longitudinal pressure
distribution is substantially uniform, the pressure sensor 50
determines that a fingerprint portion at the tip of the finger FN
is evenly placed on the image reading circuit 2, so the light
source 14 emits light to start a reading operation of the image
reading circuit 2. On the other hand, if the longitudinal pressure
distribution is not uniform but significantly biased, a fingerprint
portion at the tip of the finger FN may not be evenly touching the
image reading circuit 2. Therefore, the light source 14 does not
emit light, so a reading operation of the image reading circuit 2
is hot started.
[0061] As shown in FIG. 1, when viewed from above (in the direction
of the contact surface 32a of the image reading circuit 2), the
pressure sensor 50 and image reading circuit 2 are arranged in
different positions. More specifically, the pressure sensor 50 is
formed adjacent to the image reading circuit 2. The surface of the
pressure sensor 50 is on the same level as the contact surface 32a
of the image reading circuit 2. This surface of the pressure sensor
50 and the contact surface 32a form a placement surface on which
the finger FN is to be placed.
[0062] The finger holder 16 will be explained below.
[0063] In the finger holder 16, an opening or a hole 16a is formed
into the shape of a finger from the tip of the finger FN to its
second joint, as shown in FIG. 3. The finger holder 16 is attached
to the contact surface 32a of the image reading circuit 2 and the
surface of the pressure sensor 50, so that the image input region 8
in which the sensor elements 20 are arranged and a pressure sensing
region in which the intersections of the electrode lines 51 and 52
are arranged are exposed to the opening. That opening of the finger
holder 16, which corresponds to a finger pad is formed in the image
input region 8.
[0064] The circuit configuration of the fingerprint reader 1 will
be described below with reference to FIG. 5.
[0065] As shown in FIG. 5, the fingerprint reader 1 includes the
sensing circuit 61, a comparison circuit 62, a CPU 63, a RAM 64, a
ROM 65, and a storage unit 66, in addition to the image reading
circuit 2, driving circuit 10, and pressure sensor 50.
[0066] The sensing circuit 61 drives the pressure sensor 50 to
receive an electrical characteristic change or changes of a signal
output to at least one of the electrode lines 51 and 52 of the
pressure sensor 50, and outputs, to the comparison circuit 62, a
sense signal indicating the level of the whole longitudinal
pressure sensed by the pressure sensor 50. The sensing circuit 61
also outputs, to the CPU 63, pressure distribution data indicating
the pressure distribution sensed by the pressure sensor 50.
[0067] The comparison circuit 62 receives the sense signal from the
sensing circuit 61, and compares the level of the sense signal with
a threshold value which discriminates between a finger placed state
and finger unplaced state. If the sense signal level exceeds the
threshold value, the comparison circuit 62 outputs a trigger signal
to the driving circuit 10.
[0068] A sensing means comprises the pressure sensor 50, sensing
circuit 61, and comparison circuit 62 described above. The sensing
means senses, on the basis of the pressure applied to the surface
of the pressure sensor 50, that the finger FN is placed on the
contact surface 32a of the image reading circuit 2.
[0069] When receiving the trigger signal from the comparison
circuit 62, the driving circuit 10 first outputs a signal for
causing the light source 14 to emit light, thereby causing the
light source 14 to emit light. After that, the driving circuit 10
outputs the control signal Bcnt to the bottom gate driver 12, the
control signal Tcnt to the top gate driver 11, and the control
signal Dcnt to the data driver 13. Consequently, the image reading
circuit 2 starts operating. When the image reading circuit 2 thus
operates, the driving circuit 10 acquires a fingerprint image of
the finger FN, and outputs the fingerprint image data to the CPU
63.
[0070] The storage unit 66 stores registered fingerprint image data
of a finger pad of each registrant. In addition to the area for
storing the registered fingerprint image data, the storage unit 66
also has a data storage area storing various data. This data
storage area has a specific area and normal area. The registered
image data can be data representing the relative positions of a
plurality of feature points extracted from a fingerprint, or an
image itself.
[0071] The ROM 65 stores programs executable by the CPU 63. The CPU
63 operates in accordance with these programs stored in the ROM 65
by using the RAM 64 as a work area. For example, the CPU 65
receives fingerprint image data from the-driving circuit 10,
receives pressure distribution data from the sensing circuit 61,
checks on the basis of the input pressure distribution data whether
an object placed on the surface of the pressure sensor 50 can be
regarded as a middle part of a finger, and, if an object placed on
the surface of the pressure sensor 50 can be regarded as a middle
part of a finger, compares the input fingerprint image data from
the driving circuit 10 with the registered fingerprint image data
stored in the storage unit 66, thereby checking whether the
fingerprint image data can be regarded as matching the registered
fingerprint image data. If the CPU 63 determines that the
fingerprint image data can be regarded as matching the registered
fingerprint image data, it starts a secrete mode. If the CPU 63
determines that the fingerprint image data cannot be regarded as
matching the registered fingerprint image data, it starts a normal
mode.
[0072] The operation of the fingerprint reader 1 of this embodiment
and a method of using the same will be explained below.
[0073] When nothing is in contact with the surface of the pressure
sensor 50, the level of a sense signal indicating the whole
longitudinal pressure sensed by the pressure sensor 50 is less than
a threshold value. Therefore, the comparison circuit 62 outputs no
trigger signal to the driving circuit 10.
[0074] On the other hand, as shown in FIG. 2A, when a person to be
examined places a finger pad of the finger FN on the contact
surface 32a of the antistatic film 32 and at the same time places a
middle part of the finger FN on the surface of the pressure sensor
50, the light source 14 emits light. Output light from the
diffusion light-guiding plate 15 is incident on the finger FN via
the image reading circuit 2, and reflected light from the finger FN
enters the semiconductor films 23 of the sensor elements 20. The
longitudinal intensity distribution of the reflected light entering
the semiconductor films 23 of the sensor elements 20 matches
projections and recesses of the fingerprint of the finger FN. The
light from the light source 14, which is incident on the
projections of the finger FN in close contact with the contact
surface 32a propagates in the skin of the finger FN and finally
scatters toward the sensor elements 20 positioned below these
projections. This scattered light having high intensity enters the
semiconductor films 23 of the sensor elements 20 to generate
electron-hole pairs. In the recesses of the finger FN which are
separated from the contact surface 32a, the light is entrapped into
the space between these recesses and the contact surface 32a, and
attenuates by repeating irregular reflection between the recesses
and space. Accordingly, no sufficient light is reflected toward the
semiconductor films 23 of the sensor elements 20 below these
recesses, so electron-hole pairs are not sufficiently
generated.
[0075] Since the middle part of the finger FN is placed on the
pressure sensor 50, a pressure is applied from the finger FN to the
pressure sensor 50. If this pressure reaches such an extent that
the finger FN well presses the pressure sensor 50, some of pressure
sensing points at the intersections of the electrode lines 51 and
52 of the pressure sensor 50 are rendered conductive to produce
potential changes. If the number of these conductive portions of
the pressure sensing points reaches a predetermined number, the
pressure level of a sense signal reaches the threshold value, so
the comparison circuit 62 outputs a trigger signal to the driving
circuit 10.
[0076] When receiving this trigger signal from the comparison
circuit 62, the driving circuit 10 first outputs a signal for
causing the light source 14 to emit light, so the light source 14
irradiates the contact surface 32a with light. Then, the driving
circuit 10 outputs the control signal Tcnt to the top gate driver
11, the control signal Bcnt to the bottom gate driver 12, and the
control signal Dcnt to the data driver 13.
[0077] In each of the sensor elements 20 in a predetermined row of
the image reading circuit 2, a relatively positive voltage reset
signal from the top gate driver 11 is applied to the top gate
electrode 30 to discharge holes stored in the semiconductor film 23
and channel protective film 24 up to this point. Subsequently, a
voltage of -20 (V) is applied to the top gate electrode 30 with the
bottom gate electrode 23 held at 0 (V), thereby starting reading
the reflected light from those projections and recesses of the
finger FN, which form the fingerprint.
[0078] Since the projections of the finger FN are in contact with
the contact surface 32a, these projections efficiently reflect the
light from the light source 14 toward the semiconductor films 23 of
the sensor elements 20 positioned below the projections, thereby
generating a large amount of electron-hole pairs. Of these
electron-hole pairs, only positively charged holes are trapped in
the semiconductor films 23 and channel protective films 24 by a
negative electric field applied to the top gate electrodes 30, and
electrons are repelled by this electric field and discharged
outside the sensor elements 20. On the other hand, the recesses of
the finger FN are not in contact with the contact surface 32a.
Therefore, the light from the light source 14 is irregularly
reflected by the low-refractive-index space between the recesses
and contact surface, and hence does not enter the semiconductor
films 23 of the sensor elements 20 positioned below these recesses.
As a consequence, holes are not sufficiently stored in the
semiconductor films 23 and channel protective films 24.
[0079] The data driver 13 outputs a high-level, pre-charge signal
to all the data lines 43 to cause them to hold a predetermined
voltage.
[0080] When a predetermined time has elapsed since a voltage of -20
(V) is applied to the top gate electrodes 30, the bottom gate
driver 12 applies a voltage of +10 (V) to the bottom gate
electrodes 21. In this state, no sufficient light enters the sensor
elements 20 positioned below the recesses of the finger FN and the
sensor elements 20 below a portion where the finger FN is not
placed, so no holes are stored in the semiconductor films 23 and
channel protective films 24. In each semiconductor film 23,
therefore, that electric field generated by the voltage of +10 (V)
from the bottom gate electrode 21, which forms a channel is
canceled by that electric field generated by the voltage of -20 (V)
from the top gate electrode 30, which erases a channel.
Consequently, a depletion layer extends in the semiconductor film
23 to allow no electric current to flow in the source-to-drain
path, so the pre-charge voltage on the data line 43 is
maintained.
[0081] Since the reflected light from the light source 14 well
enters each sensor element 20 positioned below the projections of
the finger FN, holes are stored in the semiconductor film 23 and
channel protective film 24. These holes are attracted to the top
gate electrode 30 by the electric field of -20 (V), and at the same
time cancel the negative electric field of the top gate electrode
30 by the charge amount of the holes. Therefore, no channel is
formed when the bottom gate electrode 21 is at 0 (V). However, when
the bottom gate electrode 21 changes to +10 (V), the electric field
of the bottom gate electrode 21 and the positive electric field
generated by the stored holes become larger than the negative
electric field of the top gate electrode 30, thereby forming a
channel in the semiconductor film 23. Consequently, an electric
current flows from the drain electrode 28 set at a high potential
by the pre-charge voltage to the grounded source electrode 27, so
the potential of the data line 43 lowers.
[0082] By reading that voltage drop on the data line 43, which
changes in accordance with the presence/absence of incidence of
light, the data driver 13 can detect a projection or recess of a
finger. The above series of operations from the output of the reset
signal to the read of the potential of the data line 43 are
performed row by row.
[0083] The CPU 63 checks whether the input fingerprint image data
from the sensor element 20 can be regarded as matching the
registered fingerprint image data in the storage unit 66. If the
CPU 63 determines that the fingerprint image data matches the
registered fingerprint image data, the CPU 63 starts a secrete
mode. In this secrete mode, the CPU 63 can access the specific area
and normal area in the storage unit 66, or door lock or the like is
unlocked. If the CPU 63 determines that the fingerprint image data
does not match the registered fingerprint image data, it starts a
normal mode. In this normal mode, the CPU 63 can access the normal
area and cannot access the specific area in the storage unit 66, or
door lock or the like is not unlocked.
[0084] The effects of this embodiment will be explained below.
[0085] Only by placing a portion from the first joint to the tip of
the finger FN on the contact surface 32a of the image reading
circuit 2 and at the same time placing a portion from the second
joint to the first joint of the finger FN on the surface of the
pressure sensor 50, it is possible to detect that the finger is
placed and start reading a fingerprint image. Therefore,
fingerprint reading can be simply started without causing a person
to be examined to perform two steps, i.e., place his or her finger
on a predetermined portion and press a button for starting
fingerprint authentication. Also, since the image reading circuit 2
does not operate unless the finger FN is placed, the power
consumption can be reduced.
[0086] As shown in FIG. 2B, at substantially the same time the
finger FN is placed on the surface of the image reading circuit 2,
a middle part of the finger FN is also placed on the surface of the
pressure sensor 50 to apply a pressure from the finger FN to the
pressure sensor 50. If a finger pad having a fingerprint of the
finger FN is not placed in a broad range of the contact surface 32a
of the image reading circuit 2, a voltage change indicates that the
longitudinal pressure distribution on the contact surface 32a is
biased, even when a sufficient pressure is applied to a few
pressure sensing points. Accordingly, the pressure level of a sense
signal does not reach a threshold value, so the image reading
circuit 2 performs no image reading. This prevents an unclear image
from being read. Since the light source 14 does not emit light, a
person to be examined can see no light from the light source 14, so
he or she notices that the image reading circuit 2 is not
performing a reading operation.
[0087] If the person to be examined thus notices that the image
reading circuit 2 is not performing a fingerprint reading operation
because the finger FN is not pressed with a sufficient force
against the image reading circuit 2 or the finger pad having the
fingerprint is not in contact with a broad range of the contact
surface 32a of the image reading circuit 2, it is possible to
prompt the person to strongly press the finger FN against the image
reading circuit 2 and pressure sensor 50 and press the finger pad
having the fingerprint against a broad range. When the person
presses the finger FN with a sufficient pressure against a broad
range of the pressure sensor 50 so that the number of conductive
portions of a plurality of pressure sensing points reaches a
predetermined number, the pressure level of a sense signal reaches
the threshold value, and the comparison circuit 62 outputs a
trigger signal to the driving circuit 10, so the image reading
circuit 2 starts reading the fingerprint. Since clear fingerprint
image data can be reliably read, accurate authentication can be
performed.
[0088] If the projections of the finger FN are not in close contact
with the contact surface 32a of the image reading circuit 2, the
contact pressure level between the finger FN and the surface of the
pressure sensor 50 is lower than the threshold value. Therefore, a
fingerprint image may become unclear if it is read in this state.
However, the image reading circuit 2 does not perform an image
reading operation unless the level of a sense signal indicating the
pressure applied from the finger FN to the surface of the pressure
sensor 50 is equal to or higher than the threshold value.
Accordingly, no unclear fingerprint image data is read owing to
insufficient pressing. In contrast, the image reading circuit 2 can
reliably read a clear fingerprint image while a pressing force is
applied to such an extent that the pressure sensor 50 can determine
that it is pressed by the finger FN.
[0089] By setting the upper and lower limits of the threshold level
of the comparison circuit 62, it is possible to allow the image
reading circuit 2 to perform an image reading operation only when
the contact pressure between the finger FN and the surface of the
pressure sensor 50 falls within an appropriate range. This
eliminates the inconvenience that optical fingerprint
discrimination is made difficult to perform, or the fingerprint
forms a distorted image to make accurate authentication impossible,
because the difference between the heights of the projections and
recesses of the finger FN is decreased by too strong pressing of
the finger FN against the image reading circuit 2.
[0090] [Second Embodiment]
[0091] A fingerprint reader 101 different from the fingerprint
reader 1 of the first embodiment will be described below with
reference to FIGS. 6A to 8.
[0092] In the second embodiment, a diffusion light-guiding plate 15
overlaps an image reading circuit 2, and that surface of the
diffusion light-guiding plate 15, which faces the rear surface of
the image reading circuit 2 is in contact with the rear surface of
the image reading circuit 2.
[0093] In the above first embodiment, the surface of the pressure
sensor 50 is on the same level as the contact surface 32a of the
image reading circuit 2. In the second embodiment, however, a
pressure sensor 50 overlaps the diffusion light-guiding plate 15,
and the surface of the pressure sensor 50 is in contact with the
rear surface of the diffusion light-guiding plate 15. That is, the
fingerprint reader 101 is obtained by stacking the pressure sensor
50, diffusion light-guiding plate 15, and image reading circuit 2
in this order from below. Therefore, a pressure applied to a
contact surface 32a of the image reading circuit 2 is also applied
to the pressure sensor 50, so the pressure sensor 50 can sense the
pressure on the contact surface 32a of the image reading circuit 2.
The pressure sensor 50 includes a plurality of electrode lines 51
formed on a substrate 56 and running parallel to each other in the
row direction, a flexible sheet member 55 on the rear surface of
which a plurality of electrode lines 52 running parallel to each
other in the column direction are formed, and a seal 54 which
covers the perimeter of the sheet member 55 and adheres the
substrate 56 and sheet member 55. The electrode lines 52 are
separated from the electrode lines 51. The sheet member 55 and
substrate 56 are adhered such that the electrode lines 51 and 52
are perpendicular to each other when viewed from above and oppose
each other. A pressure-sensitive ink layer may also be formed on
the surface of at least one of the electrode lines 51 and 52. In
this case, pressure-sensitive ink layers overlap each other at the
intersections of the electrode lines 51 and 52. The electrical
resistance between the electrode lines 51 and 52 depends upon a
pressure applied to the pressure-sensitive ink layers; if the
pressure changes, the electrical resistance or the like also
changes. In the pressure sensor 50, the pressure at each
intersection of the electrode lines 51 and 52 can be sensed by the
electrical resistance or the like at the intersection.
[0094] In addition to the circuit configuration shown in FIG. 5,
the fingerprint reader 101 of the second embodiment has an
adjusting circuit 102 for adjusting the light emission intensity of
a light source 14 as shown in FIG. 8.
[0095] Referring to FIG. 8, a sensing circuit 61 outputs, to a
comparison circuit 62, a sense signal indicating the level of the
whole longitudinal pressure sensed by the pressure sensor 50. If
the pressure level is within an allowable range over which a finger
can be recognized, the comparison circuit 62 outputs, instead of a
trigger signal, a pressure information signal indicative of this
pressure level to a driving circuit 10. In accordance with the
pressure level of this pressure information signal, the driving
circuit 10 outputs a light emission gradation signal of the light
source 14 to the adjusting circuit 102. The adjusting circuit 102
causes the light source 14 to emit light at brightness
corresponding to the light emission gradation signal. That is, the
adjusting circuit 102 causes the light source 14 to start light
emission in accordance with the pressure level, and adjusts the
level of electric power to be supplied to the light source 14 on
the basis of the pressure level, thereby adjusting the light
emission intensity of the light source. After the light source 14
emits light, the driving circuit 10 outputs a control signal Bcnt
to a bottom gate driver 12 to cause the bottom gate driver 12 to
appropriately output a read signal, outputs a control signal Tcnt
to a top gate driver 11 to cause the top gate driver 11 to
appropriately output a reset signal, and outputs a control signal
Dcnt to a data driver 13 to cause the data driver 13 to
appropriately output a pre-charge signal. The driving circuit 10 is
so set that if the pressure level of the pressure information
signal from the comparison circuit 62 falls within the allowable
range and is low (the pressing force is small), the driving circuit
10 outputs, to the adjusting circuit 102, a light emission
gradation signal by which the emission illuminance of the light
source 14 decreases, and, if the pressure level of the pressure
information signal from the comparison circuit 62 falls within the
allowable range and is high (the pressing force is large), the
driving circuit 10 outputs, to the adjusting circuit 102, a light
emission gradation signal by which the emission illuminance of the
light source 14 increases.
[0096] The constituent elements of the fingerprint reader 101 are
the same as those of the fingerprint reader 1 except for those
described above. Therefore, a detailed explanation of the image
reading circuit 2, the pressure sensor 50, the sensing circuit 61,
a CPU 63, a RAM 64, a ROM 65, and a storage unit 66 will be
omitted.
[0097] The operation of the fingerprint reader 101 and a method of
using it will be explained below.
[0098] When nothing is in contact with the contact surface 32a of
the image reading circuit 2, as shown in FIG. 6A, the level of a
sense signal output from the sensing circuit 61 to the comparison
circuit 62 is low. Therefore, the comparison circuit 62 outputs no
pressure information signal to the driving circuit 10, so the
driving circuit 10 does not allow the light source 14 to emit light
via the adjusting circuit 102.
[0099] On the other hand, as shown in FIGS. 6B and 7, when a person
to be examined places a finger pad of the finger FN on the contact
surface 32a of an antistatic film 32, a pressure is applied from
the finger FN to the pressure sensor 50 via the image reading
circuit 2. Since the pressure level of a sense signal output from
the sensing circuit 61 to the comparison circuit 62 is high, the
comparison circuit 61 outputs, to the driving circuit 10, a
pressure information signal containing recognition information
indicating that the finger is placed and information indicating the
degree of the pressing force, in accordance with the pressure level
of the sense signal. In accordance with this pressure information
signal, the driving circuit 10 outputs a light emission level
signal to the adjusting circuit 102. On the basis of this light
emission level signal, the adjusting circuit 102 causes the light
source 14 to emit light with predetermined brightness. In this
processing, the adjusting circuit 102 increases the light emission
intensity of the light source 14 on the basis of the information of
the light emission level signal, i.e., when the pressing force on
the contact surface 32a of the image reading circuit 2 is low or
decreases. If the output sense signal from the sensing circuit 61
to the adjusting circuit 102 becomes equal to or lower than the
level when nothing is placed on the antistatic film 32, i.e.,
becomes equal to or lower than the level when no pressure is
applied to the pressure sensor 50, the adjusting circuit 102 turns
off the light source 14.
[0100] When the light source 14 emits light, this light is incident
on the finger FN from the diffusion light-guiding plate 15 via the
image reading circuit 2, thereby causing reflection and scattering
on the finger FN. Although large amounts of reflected light and
scattered light enter the sensor elements 20 positioned below
projections of the finger FN, neither reflected light nor scattered
light sufficiently enters the sensor elements 20 positioned below
recesses of the finger FN.
[0101] After outputting the light emission gradation signal to
cause the light source 14 to emit light, the driving circuit 10
outputs control signals to the drivers 11, 12, and 13 of the image
reading circuit 2. The drivers 11, 12, and 13 transfer an
electrical signal corresponding to the intensity of reflected light
entering the sensor elements 20 in the image reading circuit 2 to
the driving circuit 10 via the data driver 13. The driving circuit
10 acquires a fingerprint image of the finger FN by sensing the
level of the electrical signal, and outputs the fingerprint image
data to the CPU 63. The CPU 63 checks whether the input fingerprint
image data can be regarded as matching registered fingerprint image
data in the storage unit 66. If the fingerprint image data can be
regarded as matching the registered fingerprint image data, the CPU
63 initiates a secrete mode. If the fingerprint image data cannot
be regarded as matching the registered fingerprint image data, the
CPU 63 initiates a normal mode.
[0102] The effects of this embodiment will be explained below.
[0103] When the pressure of the finger FN is small or decreases,
the contact area between projections of the finger FN and the
contact surface 32a decreases. If this projections are not in close
contact with the contact surface 32a any longer, low-intensity
reflected light from the projection may enter the semiconductor
film 23. However, since the light emission intensity of the light
source 14 increases as the pressure of the finger FN decreases, the
intensity of light incident on the finger FN also increases.
Therefore, even when a projection of the finger FN is not in close
contact with the contact surface 32a, high-intensity reflected
light from the projections enters the semiconductor film 23.
[0104] Also, if the light emission intensity of the light source 14
is high even though the pressure of the finger FN is also high,
high-intensity reflected light from recesses of the finger FN
enters the semiconductor film 23. Consequently, the longitudinal
intensity distribution of the reflected light entering the
semiconductor films 23 of the sensor elements 20 becomes
substantially uniform and bright. However, no such problem arises
because the light emission intensity of the light source 14
decreases as the pressure of the finger FN increases.
[0105] In this embodiment, therefore, the image reading circuit 2
can clearly read a fingerprint image of the finger FN regardless of
the pressure of the finger FN.
[0106] Also, the fingerprint reader 101 of the second embodiment
achieves the same effects as the fingerprint reader 1 of the first
embodiment.
[0107] The image input apparatus as described above can be applied
as a person authentication system at a doorway or as an individual
identification image input apparatus for restricting access to a
personal computer or the like. The image input apparatus is
particularly effective in a compact portable apparatus, such as a
cell phone, notebook PC, or PDA, whose power consumption and size
are limited.
[0108] Similar to the fingerprint reader 101 of the second
embodiment, the fingerprint reader 1 of the first embodiment may
also have the adjusting circuit 102 for adjusting the light
emission intensity of the light source 14 as shown in FIG. 8, in
addition to the circuit configuration shown in FIG. 5.
[0109] The present invention is not limited to the above
embodiments and can be variously improved or changed in design
without departing from the spirit and scope of the invention.
[0110] In each of the above embodiments, the finger FN is read.
However, various other objects to be examined may also be pressed
against the contact surface 32a of the antistatic film 32 and read,
as well as the finger FN. By pressing an object to be examined
against the contact surface 32a of the antistatic film 32, the
image reading circuit 2 can read a pattern (including, e.g.,
characters, numerals, and pictures) drawn on the surface of the
object, or a pattern defined by projections and recesses on the
surface of the object.
[0111] In each of the above embodiments, the contact surface 32a of
the antistatic film 32 is a placement surface on which an object to
be examined is placed. However, this placement surface may also be
the surface of an insulating film formed on the antistatic film 32.
Also, the antistatic film 32 may be omitted.
[0112] The fingerprint reader 101 of the second embodiment having
the structure in which the pressure sensor 50 is placed below the
image reading circuit 2 need not always have the adjusting circuit
101 as shown in FIG. 8, but may also have the circuit configuration
shown in FIG. 5. Likewise, the fingerprint reader 1 of the first
embodiment having the structure in which the pressure sensor 50 is
placed so as not to overlap the image reading circuit 2 need not
always have the circuit configuration as shown in FIG. 5, but may
also have the circuit configuration shown in FIG. 8.
[0113] Each of the above embodiments has been explained by taking
the image reading circuit 2 using the sensor elements 20 as
photoelectric conversion elements as an example. However, the
present invention is also applicable to an image reading circuit
using photodiodes as photoelectric conversion elements. Examples of
the image reading circuit using photodiodes are a CCD image sensor
and CMOS image sensor.
[0114] In the CCD image sensor, photodiodes are formed pixel by
pixel in a matrix manner on a substrate. Around each photodiode, a
vertical CCD and horizontal CCD for transferring an electrical
signal photoelectrically converted by the photodiode are
formed.
[0115] In the CMOS image sensor, photodiodes are formed pixel by
pixel in a matrix manner on a substrate. Around each photodiode, a
pixel circuit for amplifying an electrical signal photoelectrically
converted by the photodiode is formed.
[0116] Furthermore, an image such as a fingerprint may also be read
by a non-optical sensor which reads an electrical characteristic
change caused by the electrostatic capacity unique to a finger,
instead of the optical sensor described above.
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